W.O. Barnard

Comparative study of surface properties of austenitic stainless steels in sulfuric and hydrochloric acid solutions

In this work, time, concentration and potential dependence of Cl− and HSO4−SO42− accumulations on two austenitic stainless steels (AISI 316L + 0.5%Ru and 08X18H10T (GOST 5632-61) which corresponds to AISI 304) are studied by an in situ radiotracer method and voltammetry. Several independent techniques such as XPS and ICP-OES are also used to characterize the complex features of the passivation and dissolution of steels with and without Mo and Ru as additives. From the experimental results, it is obvious that the surface excess values of bisulfate/sulfate ions on both stainless steels are much higher (up to Γ = 1.5 × 10−9 mol cm−2) and their interaction with the passive oxide layer is substantially stronger than those of chloride ions. The surface concentration of Cl− of less than 2 × 10−10 mol cm−2 (if any) provides evidence that only a very limited part of the real surface area of the steel samples (less than 5%) is occupied by Cl− ions, ie, pitting corrosion sites are probably formed. Some possible links between sorption phenomena and the structure and chemical composition of passive layers are also presented and discussed.

Surface composition of Ru containing duplex stainless steel after passivation in non-oxidizing media

Abstract In this paper, results obtained by surface analysis (Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS)) studies performed on the passive layers that formed spontaneously on duplex stainless steels (DSSs) and Ru containing (0.3%) duplex stainless steel (DSS:Ru) in HCl and H 2 SO 4 solutions are presented in order to explain the roles of the different alloying elements in the passivation process. From the AES studies, it followed that the Cr concentrations were slightly higher (about 3%) in the passive layers of both materials, compared to their bulk concentrations, whereas the Ni concentrations were reduced to less than half their bulk concentrations at the outer surfaces of the passive layers, with an increasing concentration gradient towards the bulk of the material. Enrichment of Mo at outer surface of the passive layer was only observed in the case of the DSS:Ru samples which were passivated in HCl. The XPS results indicated that the passive layer on the DSS:Ru samples contained more Cr 2 O 3 and Fe 2+ than Cr(OH) 3 and Fe 3+ , respectively, in the passive layer, compared to the DSS samples without Ru.

Corrosion behaviour of duplex stainless steels containing minor ruthenium additions in reducing acid media

The dissolution behaviour, as well as the time, potential and concentration dependence of HSO−4SO2t-4and Cl− accumulations measured by an in situ radiotracer method on surface oxide-layers of duplex stainless steels containing various amounts of ruthenium as additive are presented and discussed. Several independent techniques, such as mass loss tests, potentiodynamic responses, radiotracer and ICP methods, were used to characterize the complex features of the passivation phenomena of steels modified with ruthenium. The experimental results reveal that the interaction of bisulfate/sulfate ions with passive oxide layer is stronger than those of chloride ions on the stainless steels studied. Both the extent and the strong character of bisulfate/sulfate accumulation are more likely related to the redistribution of the main alloying components (Cr, Ni, Mo) as well as the Ru in the surface oxide-film formed on steels passivated spontaneously in dilute HCl and H2SO4. It is found that the ruthenium additions to the base duplex stainless steel significantly increase the corrosion resistance in reducing acid environments. There is evidence of anodic inhibition and this seems to be responsible for the observed increased corrosion resistance of the duplex stainless steels with small ruthenium additions.

Electrical characterization of neutron irradiation induced defects in undoped epitaxially grown n-GaAs

Undoped n‐GaAs, grown by organometallic vapor phase epitaxy, was irradiated with neutrons from a clinical p(66)/Be(40) source for a range of fluences. Deep level transient spectroscopy (DLTS), employing Pd Schottky barrier diodes, indicated that four electron traps, En1, En2, En4, and En5, with energy levels at 0.04, 0.14, 0.36, and 0.66 eV, respectively, below the conduction band were created during neutron radiation. Their introduction rates varied from 1 cm−1 for the En1 to 11 cm−1 for the En5. It was found that the En1, En2, and En4 defects have DLTS ‘‘signatures’’ similar to the E1, E2, and E3 point defects introduced during high energy electron irradiation, indicating their point defect nature. The En5 has a very large capture cross section, its emission rate exhibits a strong electric field dependence, and there are indications that it has a band‐like energy distribution, that results in a broad DLTS peak. We speculate that this trap is related to the presence of extended defects in the neutron irr...

Vacuum annealing characteristics of electron beam evaporated ruthenium contacts to n-GaAs grown by organometallic vapour phase epitaxy

Abstract High quality ruthenium Schottky barrier diodes were fabricated on organometallic vapour phase epitaxially grown n-GaAs, with a carrier density of 1 x 10 16 cm −3 , by electron beam evaporation of ruthenium at a rate of 1 A s −1 . The annealing studies were carried out in vacuum over the temperature range from 225 °C to 600 °C. The electrical characteristics of the Schottky contacts were evaluated by standard current-voltage I–V and capacitance-voltage C–V measurements. The effective barrier height ϕ e I–V and the flat band barrier height ϕ b C–V of the as-deposited R u-n-GaAs Schottky contacts were 0.865 eV and 0.916 eV respectively. These barrier heights reached their respective maximum values of 0.925 eV and 0.955 eV after annealing at 450 °C. Auger electron spectroscopy results indicated that ruthenium forms structurally a very stable contact to GaAs, with no evidence of any chemical reactions between ruthenium and GaAs up to 500 °C. Very limited diffusion of arsenic through the ruthenium layer was observed after annealing at 400 °C. Diffusion of arsenic increased sharply after annealing at temperatures above 500 °C.

Effect of sputter voltage on the electrical characteristics of argon ion sputtered n-type GaAs

Abstract Epitaxially grown n-type GaAs was sputtered by bombarding it with Ar ions at voltages between 0.5 and 5 kV at a dose of 10 13 ions/cm 2 . The electrical characteristics of the sputtered GaAs were investigated by studying the sputter induced defects using deep level transient spectroscopy (DLTS). The effect of these defects on the electrical characteristics of gold (Au) Schottky barrier diodes (SBDs) was studied by current-voltage ( I–V ) and capacitance-voltage ( C–V ) measurements. It was found that the barrier height of the SBDs changed nonmonotonically with sputter voltage, and this could be correlated with the combined effect of sputter induced defects with discrete and continuous energy levels in the GaAs band gap.

The role of Ru in improving Schottky and ohmic contacts to InP

Abstract Wet chemical passivation of InP was performed in an acid solution that contained Ru ions in solution. Results showed a drastic increase in the Schottky barrier height of Ru contacts from 0.49 eV before passivation to about 0.88 eV after passivation and annealing at 125 ° C. Furthermore, a corresponding decrease in reverse leakage current of more than three orders was also obtained by passivation. The corresponding value for the ideality factor was 1.16. The higher barrier height was related to the XPS results, which showed a decrease in the amount of oxidized indium and phosphorus after passivation. Au/Ru/Au-Ge/Ni/InP ohmic contacts showed remarkable improved surface morphology after rapid thermal annealing, in comparison with the standard Au/Ni/Au-Ge/InP rapid thermal annealed (RTA) ohmic contacts. The Ru-containing contacts also showed a lower minimum specific contact resistance value of 1 × 10 −7 Ω cm 2 , after 400 ° C RTA. From comparative electrical, SEM and Auger electron spectroscopy (AES) investigations, it is clear that Ru has various advantages as a very effective diffusion barrier for ohmic contacts on InP.

Ruthenium and ruthenium-based contacts to GaAs

This paper deals with the outstanding electrical and structural properties of Ru-based Schottky and ohmic contacts fabricated by electron beam evaporation on n- and p+ -type GaAs, respectively. The effective and flatband barrier heights were evaluated by standard current-voltage (I–V)(T) and capacitance-voltage (C–V)(T) measurements, over the temperature (T) range 100 to 350 K. The modified Richardson constant, A∗∗, varied between 2.2 and 4.9 A cm−2 K-2, depending upon the annealing temperature. AES depth profiles indicated that Ru forms structurally very stable contacts to GaAs, with no evidence from XPS measurements of any compound formation between Ru and GaAs even after annealing up to 500°C. A sharp increase was observed in the formation of Ga2O3 at the interface between the Ru layer and the GaAs after vacuum annealings at temperatures of 450°C and above. Only limited diffusion of arsenic through the Ru layer was observed after annealing at 400°C, but increased rapidly above 450°C. A Au/Ru/p+-GaAs ohmic contact system showed comparable specific contact resistance (5.5×10−6 Ω·cm2) to those systems commonly used, but with superior surface morphology.

An Auger electron spectroscopy study of annealed gold contacts to InP

Abstract Auger electron spectroscopy operated in different modes was used in this study to obtain information on the annealed Au/InP system. Noticeable lateral spreading of gold contacts was observed after 400 °C annealing, with the most dramatic edge effects visible between 430 and 500 °C annealing. It was further observed that for the annealed contacts the interface region between the InP and the gold consists mostly of an AuP compound. However, the outer surface of the annealed contact contains mostly AuIn-rich compounds, together with regions where the AuP compound extends to the top surface. For contacts annealed at 500 °C a “swallow hole” occurs where the gold contact originally was. This effect is related to the decomposition of the AuP compound, with the resultant out-diffusion of phosphorus. A model is also proposed to explain the change in shape of the predominantly circular AuP mixture (at 450 °C) to the perfect square structures after 500 °C annealing.

Comparison between ruthenium‐based and other ohmic contact systems to p‐type GaAs

A conventional furnace annealed Ru/Au ohmic contact system on p‐GaAs has been investigated. Electrical and morphological characteristics of this contact system were compared with other systems such as Cr/Au, Ti/Pt, and Mn/Au. The Ru/Au contact system has been shown to have superior surface morphology and a comparable specific contact resistance value, even after annealing at 485 °C. The advantages of utilizing Ru as contact material to GaAs are that it forms high quality, thermally stable Schottky contacts to n‐GaAs and thermally stable ohmic contacts with low specific contact resistance to p‐GaAs. This dual nature of Ru contacts to GaAs makes them extremely important for future use in devices such as heterojunction bipolar transistors (HBTs) and solid state lasers.